1. Field of the Invention
The present invention pertains to a pressure support system to treat disordered breathing, and, in particular, to such a system that automatically maximizes the comfort of the respiratory treatment therapy delivered to a patient during a therapy session.
2. Description of the Related Art
It is well known that many individuals suffer from disordered breathing during sleep. Examples of sleep disordered breathing include apneas, hypopneas, flow limitations, and Chynes-Stokes respiration. Apneas can be central apneas, which is the result of a loss of a drive to breathe, obstructive apneas, which is the result of a mechanical obstruction of the airway, or mixed (central and obstructive) apneas. Obstructive sleep apnea (OSA), which is believed to be suffered by millions of people through the world, is a condition in which sleep is repeatedly interrupted by an inability to breathe, which occurs due to an obstruction of the airway; typically the upper airway or pharyngeal area. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles that stabilize the upper airway segment, thereby allowing the tissues to collapse the airway.
Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction of the airway typically results in shallow breathing, which is referred to as a hypopnea. Other types of disordered breathing include upper airway resistance syndrome (UARS), which is characterized by the absence of obstructive sleep apnea and oxygen desaturation, yet the patient experience excessive daytime sleepiness, chronic fatigue, and increased respiratory effort during sleep, leading to recurrent arousals, despite the absence of hypopneas or apneas. Still other types of disordered breathing include vibration of the airway, such as vibration of the pharyngeal wall, commonly referred to as snoring. It is also known that snoring can accompany closure of the airway leading to UARS, hypopnea, or apnea.
It is known to treat such disordered breathing by administering a respiratory treatment therapy to the patient. This therapy can take several forms. In one form, the respiratory treatment therapy involves applying a continuous positive air pressure (CPAP) to the patient's airway. This positive pressure effectively “splints” the airway, thereby maintaining an open passage to the lungs. Example of CPAP devices that provide this therapy are the REMstar® family of CPAP devices manufactured by Respironics, Inc. of Pittsburgh, Pa.
In another form, the respiratory treatment therapy involves providing a bi-level positive pressure therapy to the patient. In this treatment therapy, the pressure of fluid delivered to the patient's airway varies or is synchronized with the patient's breathing cycle to maximize the therapeutic effect and comfort to the patient. During inspiration, the patent receives an inspiratory positive airway pressure (IPAP), and during expiration, the patient receives an expiratory positive airway pressure (EPAP) that is lower than the IPAP. An example of a pressure support device that provides “bi-level” pressure support, in which a lower pressure is delivered to that patient during the patient's expiratory phase than during the inspiratory phase, is the BiPAP® family of devices manufactured and distributed by Respironics, Inc. of Pittsburgh, Pa.
It should be noted that bi-level therapies can provide pressure waveforms having a variety of different patterns. For example, the pressure can be delivered in a traditional square wave or in a fashion that more closely mimics the pressure or flow waveform of a healthy human. The term “fluid” used herein refers to any gas, mixture of gasses, or gas with medicine, etc. suitable for delivery to the airway of a human.
It is further known to provide a respiratory treatment therapy in which the pressure provided to the patient is automatically adjusted based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea, or snoring. This respiratory treatment technique is referred to as an auto-titration type of pressure support, because the pressure support device seeks to provide a pressure to the patient that is only as high as necessary to treat the disordered breathing. An example of a device that adjusts the pressure delivered to the patient based on whether or not the patient is snoring is the REMstar® Auto device manufactured and distributed by Respironics, Inc.
Other pressure support systems that offer other modes of providing positive pressure to the patient are also known. For example, a proportional assist ventilation (PAV®) mode of pressure support provides a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing effort to increase the comfort to the patient. U.S. Pat. Nos. 5,044,362 and 5,107,830 both to Younes, the contents of which are incorporated herein by reference, teach a pressure support device capable of operating in a PAV mode.
Proportional positive airway pressure (PPAP) devices deliver breathing gas to the patient based on the flow generated by the patient. U.S. Pat. Nos. 5,535,738; 5,794,615; 6,105,575; 6,609,517; and 6,932,084, (collectively referred to as “the PPAP patents”) the contents of which are incorporated herein by reference, teach a pressure support device capable of operating in a PPAP mode. Examples a device that adjusts the pressure delivered to the patient based on the patient's respiratory flow is the REMstar® Pro, Plus, or Auto with C-Flex™ or Bi-Flex® devices manufactured and distributed by Respironics, Inc. The term “C-Flex” refers to a device that provides a CPAP respiratory treatment therapy in which the pressure delivered to the patient is reduced in proportion to flow during expiration. The term “Bi-Flex” refers to a device that provides a bi-level respiratory treatment therapy in which either the IPAP or EPAP pressures are further reduced in proportion to flow.
It is also known to provide a combination of such respiratory therapies. For example, a CPAP device with C-Flex can be auto-titrating, such as REMstar® Auto with C-Flex™, so that the CPAP pressure varies during a treatment session based on the monitored condition of the patient. Similarly, a bi-level device with Bi-Flex can be auto-titrating, such as Bi-PAP® Auto with Bi-Flex™, so that the IPAP and EPAP pressures vary during a treatment session based on the monitored condition of the patient. In an auto titrating bi-level device, the difference between IPAP and EPAP, which is referred to as the pressure support (PS), can vary according to the auto-titration algorithm or it can be held constant depending on how the device is configured.
U.S. Pat. No. 6,640,806 discloses a bi-level pressure support system that automatically changes the rise-time and/or fall-time of the pressure transition between IPAP and EPAP. Changing the rise/fall time is done based on the physiological condition of the patient detected by flow, pressure, or other sensors, and may not result in an optimization of the comfort of the overall pressure support therapy.
While auto-titrating devices, bi-level device, devices that include PPAP (C-Flex or Bi-Flex), or any combination of such devices have improved on the basic CPAP device, making the respiratory treatment therapy provided to the patient more comfortable, there is still a need to further improve the comfort of the respiratory treatment therapy even further. The better the comfort, the more likely the patient is to use the therapy.